President Obama got a bounce from the Democratic National Convention, and Mitt Romney has been struggling to play catchup since. There are many reasons – and the '47 percent' comment is only one possibility.

Mitt Romney heads into the first presidential debate Wednesday night facing higher stakes than President Obama. Mr. Romney is trailing in national polls by between 3 and 4 percentage points – and more in the battleground states. The debate in Denver presents a huge opportunity, before millions of TV viewers, to change the trajectory of the race.

Why is Romney in this predicament, after running almost neck-and-neck against Mr. Obama for much of the general election campaign? The latest polls provide clues.

“Voters remain overwhelmingly pessimistic about a still sluggish economy, yet appear poised to reelect President Barack Obama because of perceptions that he understands their lives better than Republican nominee Mitt Romney and would do more to favor the middle class rather than the very wealthy,” writes Mark Blumenthal, senior polling editor of the Huffington Post.

The latest Quinnipiac national poll, released Tuesday, shows Obama ahead by 4 percentage points. The Gallup tracking poll shows Obama up by 6 points; Rasmussen has him up by 1, within the margin of error.

On Sept. 5, Obama and Romney were exactly tied in the Real Clear Politics average of national polls, at 46.8 percent each. After the Democratic National Convention, which ended the next day, Obama registered a small bounce and has never looked back.